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Appendix VI.

sides of the pulley (or brake drum) c, over the guide pullies n H.
The method is similar to that adopted in engines to measure the
brake horse-power, and to avoid vibration and jerk, a long aim
F, having weights E E upon it, is fixed to the shaft D, thus absorb-
ing the smaller changes of torque. Lastly, a worm wheel N, serves
as a. counter, and the mechanical energy produced in foot-pounds
is 2 G x 2 TT R N, where R is the radius of c in feet and N the
re^s. per min. Also the heat energy will be the weight of water
x rise of temperature, and the first result will be J times the
second. The box p is to shield A from air currents. Rowland
advanced the equivalent from 772 to 774 by this apparatus, and
still further to 778 by improving his thermometers over those
used by Joule.

P. 605,    Expansion Curve Areas : proofs.

(i) PVa   =   C

Let a gas expand in such a wa,y that its pressure-volume cunre
can be represented by the curve PV11 = C.
Taking Fig. 61-2 and remembering that:

PV11    =  PiV^   ...............................,.   (a)

P^W1   =  PaV,n.................................   (b)

p        riv_i
r   = -ysr


-  /V/ir



- w J ^


We have :


(By c)


(2) PY = C
It is required to* find the area under a rectangular hyperbola,

where P x V is constant.

p V

and    P